Inductance coil for radio frequencies



Sept. 29, 1931.

F. E. TERM AN INDUCTANCE COIL FOR RADIO FREQUENCIES I Filed June 15, 192"! llilll'll'il c gwuentoz 10 JM 0K Elflwuyo Patented Se t. 29, 1931 UNITED STATES PATENT OFFICE raanaarcx more: mum, or srmoan UNIVERSITY, ca-Lnroama muc'rmcn con. non 'mro rnnounncms This invention relates to inductance coils for radio frequencies.

The object of the present invention is to provide an inductance coil for radio frequencies which will have an exceptionally small loss. More specifically, the object of the present invention is to provide an in ductance coil in which the losses due to the phenomenon known as skin effect are substantially eliminated. v

The efi'ective resistance of an inductance coil at radio frequencies is actually many times the resistance the coil offers to direct currents. The increase in resistance for alternating currents is due to a phenomenon known as skin effect. The effect of this phenomenon causes the current to be unevenly distributed throughout the cross-section of the conductor with which the coil is wound. This uneven distribution of current means that portions of the conductor do not do their share in carrying the current so that the actual current is in reality carried by only a small part of the conductor, with the result that the energy losses are very greatly increased.

The phenomenon of skin effect arises from the eifects of eddy currents induced in the conductors of the coil. These eddy currents in turn are the result of the fact that some of the magnetic flux lines produced by the coil cut through the material of the conductor. Flux lines which encircle or .link with only a part of a complete conductor are termed partial flux linkages. These partial flux linkages induce voltages in a part of the conductor, but not in all, giving an unbalanced voltage in the conductor and this unbalanced voltagesets up eddy currents in the coil. These eddy currents are in such direction as to oppose the main current in parts of the conductor and to aid the main current in other parts so that the net result is to redistribute the current over the cross-section of the wire of the coils. The higher the freqlrliency of the alternating current, the greater t e magnitude of the skin eflect.

The present invention embodies a coil construction in which-the conductor is so shaped and oriented that the partial'flux linkages are Application fled June 15,

mar. Serial No. loam.

The present invention, together with various objects and advantages thereof, will, best be understood from a descri tion of a. preferred form or example of a 0011 embodymg the invention. For this purpose, reference is made to the accompanying drawings.

In the drawings:

Figure 1 represents a cross-section of a small coil, of ordinary construction.

Figure 2 represents a cross-section of one form of a coil embodying the present invention.

Figure 3 represents a cross-section of a modified form of a coil embodying the present invention. I

Fi re 4 represents cross-sections of wire -suita le for use in the present invention.

Figure 5 represents cross-sections of other ivvire suitable for use in the present inven- Figure 6 represents cross-sections of further wire suitable for use in the present invention, and

Figure 7 represents ther wire suitable for vention.

First referring to Figure 1, which illustrates a coil of ordinary construction, there is indicated in the drawing the approximate distribution of current density by the deepness of shading ofthe wire 2. As will be observed from such drawings, with an ordinary coil the current is concentrated on the inner surfaces of the coil windings. There is also indicated the approximate location of flux lines produced by the coil in which it will be seen that some fluxlines such as AA and BB do not completely surround all of the conductors. Such flux lines which encircle or link with only a part of a complete conductor are termed partial flux linkages. These partial flux linkages expand, contract and reverse in direction with alternating currents, cutting through and across the cross-sections of furuse 1n the present inductors can be employed;

2 metal of the wires 2, inducing voltages and edd currents therein.

ow referring to Figure 2 of the drawings, 3 indicates. a coil form which is so shape as to provide supports 4 for the coil wire 5 as to position the flat sides of the coil wire 5 parallel to the flux lines 6 developed by the coil so as to substantially eliminate partial flux "linkages.

In making the substantially cylindrical coil as indicated in Figure 3, it is thus seen it 1s necessary to wind the difierent turns at different angles.

While the preferred form of coil embodying the present invention employs a flat conductor, such as illustrated in Figure 2, oriented to make the flat side of the conductor parallel to the flux that exists at the conductor location, the invention can take a number of diiferent forms. A variety of shapes of confor example, any

' sort of a rectangular conductor is suitable to cross-section.

, conductor.

' modified form a greater or less extent.

I have illustrated in Figures '4 to 7 inclusive, several diflerent shapes of conductors. In Figure 4, the conductor 7 is of square Such a conductor is superior to a round wire. The conductors 7 7" and 7 are respectively superior to the form of the conductor 7 as the flatter and thinner the the less eddy currents will be developed therein. The conductors 8, 8, 8 and 8 of Figure 5 are substantially the same as those of Figure 4, except that the sides ofthe rectangles are wedged. These conductors are suitable for use in the coil of the present invention, generally the ones further to the right being the better.

In Figure are shown as starting with a circular shape and ending with a very flat, oval shape. The flatter the conductors of this form, the lpetter adapted for use in the present invenion.

In Figure 7, the conductors 10, 10, 10 and 10 are "represented, which have curved or moon-shaped cross-sections and are progressively thinner towards theright. When this form of conductor is employed, the curvature preferably corresponds to the curvature o theflux lines where the wire is situated, and the forms further to the right, or the flatter forms, are the better adapted for the puroses of the present invention.

Referring to Figure 3,

of coil-winding, embody ng the invention. In Figure 3, a winding form,

v or core 11, is provided,.the surface of which is curved, correspon the flux, which will Thin, flat or ding to the curvature of be developed by the coil. slightly curved wire 12 is woun against the surface of such form 11, thereby positioning the conductor or wire 12 parallel to the direction of flux developed by the coil.

' so that it 6, the conductors 9, 9 9 and 9 acting togeth such modifications an there is shown a If desired, only the inner turns of the coil may be wound in order to be parallel to the flux lines. As will be observed from the forms of the invention shown in Figures 2 and 3, the inner turns of the coil, or the turns near the center, require little or no twisting relative to the coil axis to locate the same in their proper positions. The end turns of the coil have to be twisted to a very great angle with the axis of the coil. The greatest partial flux linkages in an ordinary coil occur at the center of the coil and the losses at the center of the coil are much greater than the losses at the end turns of the coil.

In order to simplify the practical construction of the coil, some 0 the end turns thereof may be wound with round wire, as the losses thereby induced are not very great.

While the. invention has been shown as applied to a single-layer coil, it is of course obvious that it may be applied to a multi-layer coil as well.

It should also be understood that where the coil is to be encased in a shielding container,

than exists In such amust be twisted to parallel themselves with the form of flux that will exist when the coil is in the shielded container.

Preferably,

a ductile nature,

the conductor of the coil is of such as soft-drawn copper may be readily twisted into successively desired positions. Thepresent invention where several coils are used in combination; for example, as a primary and secondary coil the flux lines the conductors of the coils and the flatside of the conductors is mad to the resultant flux pro need by er wi h their currents. form'of low-loss coil for radio frequencies herein illustrated is well adapted to carry out the objects of the present invention, it is understood that further mo ifications and changes may be made in the coil without departing from the present invention, and the present invention includes all changes as come within the scope of the following appended are pro e paralle While the claims.

I claim: 1. An inductance coil comprislng a form flux lines will be arranged in ma also be applied both coils having a winding, surface substantially in line with those flux lines developed by the coil which touch such winding surface and a conductor-winding wound on said surfaces an cross-section, the

cross-section of each portion of the conductor being thus disposed substantially in line with those flux lines to traverse such portion of the coil.

, Its cross-section sotwisted that e through 60- for supporting the- 2. An inductancecoil for radio frequencies comprising a-conductor-winding of relatively flat cross-section which develo s flux lines which are non-parallel, the con uctor having each portion of the conductor lies with itsdirection of greatest breadth in direction of the flux lines developed by the coil and which traverse such portion of the conductor. a v

3. An inductance coil for radio frequencies comprising a coil wound from a conductor of relatively flat shape, each portion of the conductor-being disposed with its direction of greatest breadth substantially in line with the flux existing at the position of such portion of the conductor.

substantially parallel with the direction of the flux line at that particular point, whereby at different places on the coil where the flux line will be in different directions the flat side of the conductor is oriented in difierent directions at different places in the coil in accordance with the direction of the flux line at each location.

Signed zit-Stanford University, Cal, this 3rd day of June, 1927.

FREDERICK EMMONS TERMAN.

4; An inductance coil comprising a form having a winding surface each portion of which is substantially in linewith the fllix existing at the positionof such portion of the surface, and a conductor winding wound on said surface and having a comparatively flat I cross-sect on, the cross-section of the-conductor being thus disposed substantially in line with the flux lines existing at the position of the conductor.

5. An inductancecoil for radio frequencies comprising a conductor winding of flat'crosssection which develops flux lines which are non-parallel, the conductor having its different'portions twisted so that each portion lies substantially parallel to the flux existing at the position of that portion of the conductor.

A radio frequency inductance coil comprising a winding of conductive material having a relatively flat cross section, which wind- 5 ing is adapted when a current is assed thereto develop a magnetic field, the flux .lines of which are non-parallel, difbeing in position so that in each cross section of the winding the direction of -great est breadth of the different portions of the winding are in line with the flux lines which will be developed by the windings that pass through such portions of the winding.

radio frequency inductance coil comprising a winding of conductive material-having a relatively flat cross section, which windmg is adapted when a current is passed therethrough to develop a magnetic field, the flux lines of which are non-parallel, different portions of the conductive winding being in po'- sition so that in each cross section of the wind- 5 ing the direction ofgreatest breadth of the different portions of with the flux lines which will be develo ed by the windings that pass through sue pertions of the winding, and a supporting form winding with its cross section only disposed. i

8. A radio frequency inductance coil comprising a conductor winding in which the I conductor is a flat strip and at each point is so oriented as to have the flat side of the strip the winding are in line 40 ferent portions of the conductive winding 

